Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$42.73	6.468%	$45.4938	$45.49	$45.50	$45.50
Purchase #2	$73.71	12.398%	$82.8486	$82.85	$82.85	$82.80
Purchase #3	$246.78	7.491%	$265.2663	$265.27	$265.25	$265.30
Purchase #4	$174.69	12.187%	$195.9795	$195.98	$196.00	$196.00
Purchase #5	$183.94	6.204%	$195.3516	$195.35	$195.35	$195.40
Purchase #6	$154.36	12.705%	$173.9714	$173.97	$173.95	$174.00
Purchase #7	$40.67	12.605%	$45.7965	$45.80	$45.80	$45.80
7 purchase totals =	$916.88		$1,004.7077	$1,004.71	$1,004.70	$1,004.80